As curable organopolysiloxane compositions, compositions having condensation-curing properties and compositions having ultraviolet-curing properties are well known.
The condensation-curing type organopolysiloxane composition is cured through the condensation of an organopolysiloxane having silanol groups and an organosilicon compound having hydrolyzable groups by the action of a tin compound or a titanium compound as disclosed in, for example, JP-B-38-16798 and JP-B-40-21631. (The term "JP-B" as used herein means an "examined Japanese patent publication".) The compositions of this type cure at room temperature due to moisture in air and do not result in poor curing, being different from an addition reaction-type composition. For this reason, those compositions are used as a building sealant, a coating composition, a modeling material, a roller for a copying machine, etc.
However, the condensation-curing type organopolysiloxane composition suffers from a disadvantage that because curing is due to moisture that has penetrated thereinto, the same cannot be used as an adhesive or the like where fixed parts must be moved prior to complete curing, for example, in the case of temporarily fixing pieces to be joined, although the applied composition, including the interior thereof, will cure uniformly if it is allowed to stand for a long period of time.
On the other hand, as the ultraviolet-curing type organopolysiloxane composition, the following compositions have been proposed:
(1) a composition which comprises a vinyl group-containing organopolysiloxane and various sensitizers and which cures upon exposure to high-intensity ultraviolet rays (U.S. Pat. No. 3,726,710);
(2) a composition comprising a mercapto group-containing organopolysiloxane, methylvinyl polysiloxane and various peroxides (U.S. Pat. No. 3,816,282);
(3) a composition comprising a vinyl group-containing organopolysiloxane, an organohydrogen polysiloxane and a sensitizer (JP-B-52-40334); and
(4) a composition comprising an organopolysiloxane containing an acrylic-type unsaturated group and a sensitizer (JP-A-48-19682). (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
Those compositions all cure instantaneously when irradiated with ultraviolet rays, but have the disadvantage that the interior of the composition when it is applied thickly or parts thereof which are shadowed from the ultraviolet rays are not affected by the ultraviolet rays and remain uncured.
In order to eliminate those disadvantages of the compositions of the two types mentioned, a composition comprising a diorganopolysiloxane in which both ends of the molecule have been blocked with a hydroxyl group, a vinylsilane having a hydrolyzable group, an organosiloxane having a mercapto group, a curing catalyst and a sensitizer has been proposed as a composition having both condensation-curing properties and ultraviolet-curing properties as disclosed in, for example JP-A-60-23176. However, this composition is disadvantageous in that it emits, when reacting, the offensive odor inherent in mercapto group-containing compounds and it attacks metals, when heated, and converts them into sulfides.
Further, a composition comprising an organopolysiloxane having as a terminal group an acryldialkoxysilyl group or an acryldiallyloxysilyl group, a catalyst for moisture curing, and a photosensitizer has been proposed as disclosed in, for example, JP-A-61-127718 and JP-A-61-276810. However, the composition of this type shows poor environmental resistance such as heat resistance and low-temperature resistance, and is also disadvantageous in that it tends to undergo inhibition of curing by oxygen in air.